Radio transmitting system



March 15', 1932. R. L. DAVIS 1,849,865

RADIO TRANSMITTING SYSTEM Filed March 27, 1928 Modu/a fed Oufpuf? INVENTOR PObe/fLDQV/S.

BY 1 A %0RNEY 1 7 am High IFguency Source Patented Mar. 15, 1932 UNITED STATES PATEN- "ore ROBERT L. DAVIS, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA RADIO TRANSMITTING SYSTEM Application filed March 27, 1928. Serial No. 265,019. V

" My invention relates to radio-transmitting systems, and it has particular relation to systems of the type wherein signaling is accomplished by interrupting the continuity of a radio=carrier-wave at predetermined intervals representative of a code.

One manner in which the continuity of a carrier wave may be interrupted at signaling frequency is exemplified in the Colpitts Reissue Patent No. 15,538, February 13, 1923, wherein it is disclosed that the oscillations generated by a thermionic tube may be started and stopped at will by altering the grid-biasing potential applied therto. Sys tems of the general type of that disclosed in the Colpitts patent, however, while operative for transmitters of relatively low power, are not entirely satisfactory when an attempt is made to utilize them in connection with thermionic tubes of the power type, inasmuch as the grid-currents that must be interupted to accomplish signaling are often of such magnitude and voltage as to cause destructive sparking at the machnical-relay contacts.

In addition to the limitation as to the amount of power the Colpitts system, and others of the same general type, can satisfactorily handle, they are also incapable of extremely high-speed operation by reason of the inertia of the moving elements of the relay. The latter limitation is a serious one, inasmuch as practically all commercial radiocommunication at the presenttime is handled by machine-transmitters which attain relativelyhigh speeds. I

"It is accordingly, an'object of my invention to provide, in a radio-transmitting system,instrumentalities that shall function to permit the efficient control of higher power than has heretofore been possible. v

Another object of my invention is to provide a keying systemfor a radio-transmitter that shall be capable of handling the heavygrid currents involved in the operation of thermionic tubes of the power type.

Another object of my invention is to provide ,a grid-biasing-potential-control system that shall be particularly suitable for use in connection with thermionic amplifier and oscillator tubesof the power type. 7

Another object of my invention is to provide a keying system for radio transmitters that shall be capable of substantially unlimited speed.

Another object of my invention is to 'provide a radio-transmitting system analogous to the systemdisclosed in the aforementioned patent to Colpitts, wherein the necessity for utilizing a mechanical relay shall be elimi nated.

Another and more specific object of my in vention is to provide,-in a radio-transmitting system of the aforementioned type, a relay device for keying purposes that shall be without moving parts and, consequently, free from inertia.

According to one embodiment of my invention, I provide two separate sources of biasing potential for the'grid of one of he high-power thermionic tubes comprised in the amplifying portion of a radio-transmitting system of the type known to those skilled in the art as a master-oscillator, power-amplifier transmitter. One of the sources, preferably a direct-current generator, supplies sufficient biasing potential, when utilized alone, to maintain the grid of the thermionic tube at the normal operating potential, while the other source, which is preferably a rectifier energized from alternating-current mains, supplies enough additional potential to prevent the tube from functioning, even though supplied with grid excitation I further provide a control networkin shunt to the bias-rectifier, and include therein the plate-filament path of a second thermionic tube, which tube will hereinafter'be designated the keying tube. The input circuit of the keying tube comprises-the'secondary winding of a specially constructed keying-transformer, the primary winding of which is connected to a source of signals. I r

I find it preferable to utilize a machine controlled telegraph key, or an analogous device, as the source of signals, inasmuch as a keying system constructed according to my invention responds more eiiiciently to high-speed signals than to signals at low speeds.

The novel features that I consider characteristic of my invention'are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description of a specific embodiment, taken in connection with the accompanying drawing.

The single figure of the drawing is a schematic circuit diagram exemplifying the application of a preferred embodiment of my invention to an amplifierv stage of a radio transmitting system of the master-oscillator, power-amplifier type. I

Referring to the drawing, an amplifier stage, arranged according to my lnvention, comprises a thermionic device 1, preferably, though not absolutely necessary, of the highpower type, having a filament 2, a grid 3, and a plate 4. The filament may conveniently be energized from any source of commercial-frequency alternating current by means of a transformer 5, the secondary winding 6 of which is connected to the filament terminals. ;The grid of the device 1 is connected to an intermediate point on the secondary winding of the transformer through a radiofrequency choke coil7, a plurality of impedance devices 8, 10 and 11, and a conductor 12., A condenser 13is preferably connected in shunt to the impedance devices, which are shown in the drawing as resistors,

in order to by-pass currents at radio frequency therearound.

A ground connectionlel is provided for the conductor 12, in order to assist in stabilizing the operation of the amplifier.

Plate potential for the thermionic device 1 is supplied from a source 15, preferably a direct-current generator, over a circuit which includes an output inductor 16. The output inductor may be coupled to a succeeding amplifier stage by way of an oscillatory circuit comprising an inductor 17 and a tuning condenser 18, or coupled thereto in any one of the many ways known to those skilled in the art. If desirable, instead of utilizing additional stages of amplification between the output circuit and an antenna, the said output circuit may be directly coupled thereto. c

. A source 20 of biasing potential is arranged in shunt to the impedance device 11, the positive terminal of the source being connected to the conductor 12 which extends to the intermediate point on the secondary winding of the filament-supply transformer.

A second source 21 of biasing potential, preferably a rectifier having a filament 22 and a plate 23, is arranged in shunt to the impedance device 10, the plate 23 of the rectifier beingconnected to the end of the impedance device nearest the grid of the thermionic tube 1. The rectifier is supplied with energizing potential from a transformer 2 having two secondary windings 25 and 26, the Winding 25 serving to heat the filament and the winding 26 being connected between an intermediate point on the winding 25 and the plate to supply high potential tothe latter over the resistor 10. r v

A keying tube 27, having a filament 28 energized from=the secondary winding 30 of a power transformer 31, a grid 32, and aplate 33, is connected in shuntrto the impedance devices 8 and 10 by means of a conductor 34 which extends from an intermediate point on the secondary winding 30 to the junction between the device 8 and the choke-coil 7, and a second conductor 35 which extends from the plate 33 to the junction between thede The space-current path of vices 10 and 11. the keying tube is, therefore, in shunt to the said impedance devices 8 and 10, and is also in shunt to a portion of the output circuit of the rectifier 21.

The input circuit of the keying tube comprises the secondary 36 of a keyingtrans former 37, a stabilizing resistor 38, and a source 40 of biasing potential, the positive terminal of the latter being connected to the intermediate point on the secondary winding of the filament-supply transformer. The primarv winding 41 ofithe keying transformer 07 must have a time constant such that the inductive voltage of the transformer will not, during the time necessaryto transmit the longest single code-symbol at the minimum rate at, which the system is to operate, fall below that value necessary to so counteract the biasing source 40 that the keying tube. is rendered conductive. The minimum rate I contemplate employing is of the vorder'of from ten tofifteen words per minute, speeds.

less than thatbeing commercially impracticable.

The source of the signals is not shown, it being within the scope of my invention to utilize any well-known device for delivering direct current impulses tothe primary winding 41 at predetermined intervals anddurations in accordance with a telegraphic or other code. V

An oscillatory circuit, comprising an inductor4-2 and a tu'ning'condenser 43 connect: ed in shunt-thereto, is arranged to supply high-frequency. excitation to the power tube 1, being coupled thereto through a grid condenser la and a conductor 45. The oscillatorycircuit may be energized from a crystal, or. tuning fork-controlled master oscillator. or from any other energy source which is capable ofsupplying oscillations at the desired radiation frequency. H In the operation of a radio transmitter comprisingmy invention as herein described, the potentials of the sources 20 and 21 are so chosen that, when both sources are effective,

the power tube is suificient to bias the grid to beyond the cut-off point, thus preventing the during signal intervals.

tube from functioning as an amplifier, in spite of the continuous operation of the exciting source. The potential of the source which supplies biasing potential to the grid of the keying tube is also so adjusted that,

in the no-signal condition of the transmitters, the keying tube is biased to the cnt-ofi" point, thus preventing a flow of current therethrough from the rectifier 21. p

Code signaling is accomplished by periodically impressing on the grid of the keying tube, through the transformer 37, positive impulses of sufiicient magnitude to overcome the biasing potential supplied from the source 40, thus permitting the space-current path in the said tube tobecome sufficiently conductive to act as avshunt to the bias recti; fier 21, and also to carry the grid current from the power tube.

The shunt-path to the bias rectifier, thus established through the keying tube, includes, in addition to the resistance of the space-' current path in the said tube, the resistance of the impedance device 8; The said device serves to limit the current drawn from the rectifier by the keying tube, and it is preferably given such resistance that the grid current, plus the current from the rectifier, when flowing through the keying-tube space-cue rent path, causes a potential drop therein just sufficiently additional to the potential supplied by the bias generator to bias the grid of the power tube to its best operating value.

In one embodiment of my invention, the power tube is of the type known as WT25, rated at 250 watts, and the keying tube of the type designated 203A,. rated at watts, both of the said tubes being made by the Westinghouse Electric & Manufacturing Company. .VVhen the power tube is excited from a source of oscillatory current of sufficient amplitude, if the grid thereof is maintained at a potential 400 volts negative with respect to the filament, etficient amplification is obtained, and the grid-current flowing through the keying tube is of the orderof milliamperes. r i

The impedance devices 8, 10 and .11 are given values of 50,000, 10,000 and 2,000 ohms, respectively, the internal resistance of the bias rectifier is determined to be of the order of 2,000 ohms, and the internal resistance of the keying tube is approximately 1,666 ohms The potential developed across the bias rectifier is in the neighborhood of 1,200 volts, while the bias generator applies a potential of 200 volts across the terminals of the impedance device 11.

The cut-off potential applied to the grid of the power tube, when the keying tube is blocked from the source 40, is substantially 1,200 volts, which is amply suflicient to prevent any excitation of the said power tube from the master oscillator. The current fiow ing in the keying tube during signal intervals is approximately milliamperes, producing a potential-drop thereacross of approximately 200 volts.

My invention is mainly advantageous in that the keying speed obtainable by its use is inno 'manner limited by the inertia of mechanlcal relay devices. The response of the keying tube, and the consequent startingand stopping of the amplification in the power tube, is substantially instantaneous, thus giving rise to radiated signals that are clean cut and easily readable. I

The current carried by the keying tube, 120 milliamperesin the specific arrangement herein described, is well within the limits or" safety for the device, and it is believed obvious that, for the handling of higher currents, keying tubes of could be utilized.

Although I have described my invention as being particularly adapted to be incor,,

porated into a power-amplifier stage of a radio transmitting system of the master-oscillator, power-amplifier type, it is not, in reallty, restricted thereto. It lies within the province of my invention to apply my improved keying system to the master oscillator itself, or to apply it to any oscillation generator or amplifier when it is desirable to interrupt the continuity of the generated oscillations or their amplification.

Inasmuch as numerous modifications of my inventionwill be apparent to those skilled in the art, it is my desire that its scope shall not be restricted except insofar as is necessitated by the prior art or by the spirit of the appended claims. 7 r

I claim as my invention 1. In a signaling system, an electronic de-' vice having a control electrode, a circuit network associated with said control electrode and including a plurality of means for-apply ing a blocking potential thereto, electronic means for rendering ineffective a portion of said potential-applying means, and signal actuated means for altering the conductivity of said second-mentioned electronic means, said electronic means being connected in shunt to a portion of said circuit.

2. In a signaling system, an electronic device having a control electrode, a circuit net.- work associated with said control electrode and including a plurality of means for applying a blocking potential thereto, a second network connectedin shunt to a portion of said potential-applying means, an electronic device included in said second network, and signal-actuated means for altering the conmuch larger capacity vice having a control electrode, a circuit network associated with said electrode: and including a plurality of sources of biasing potential having a total magnitude suificient to render the saidele'ctronic device inoperative if applied to the said control electrode,

and an electronic device connected in shunt to at least one of said sources for altering the effectiveness thereof.

5. In asignaling system, an electronic device having a control electrode, means comprising a source of potential and a resistor for applying a biasing potential to said electrode, and electronic [means connected in shunt relation to said source andin-series relation to said resiston,

6. In a signaling system, an electronic de Vice having a control-electrode and a source of electrons, means comprising source of potential and a resistor connected serially between said electrode and said source of elecg trons for applying a biasing potential to sa d electrode, and electronic means connected in shunt relation to said source and in series relation to said resistor.

7. In a signaling system, a thermionic device having a grid and a filament, grid-biasing means comprising a potential source and a resistor serially connected between said grid and said filament, a second thermionic de vice connected in shunt relation to said source and in series relation to said resistor, and signal-actuated means for altering the conductivity of said second-mentioned thermionic device.

8. Ina signaling system, a thermionic device having a grid and a filament, a network 7 including a plurality of'sources of biasing potential and a plurality otimpedance devices connected between'said grid and said filament, and a second thermionic device so interposed in said network that its space-current path is connected in shunt relation toat least one of said sources and in series relation to at least one of said impedance devices- 9. In a signaling system, a thermionic device having a grid and a filament, a network including a plurality of sources of biasing potential and a plurality of impedance devices connected between said grid and said filament, a second thermionic device so interposed in said network that its space-current v path is connected in shunt relation to at least one of said sources and in series-relation to at least one of sa1d impedance devices, and signal-actuatedmea-ns for altering the conduc= tivity of saidfsecond-mentioned thermionic devicef, i

10. In a vice having a gridand a filament and being of the type wherein a substantial grid current flows during 1 the operation thereof, means for applying a negative potential between said grid and said filament, and a second thermionic device connected in shunt to a portion of said'mean's for rendering more positive said potential and for carrying the grid current when the potential is made sufficiently positive to permit saidgrid current toflow, whereby the operation of said first mentioned thermionic device may be controlled without the destructive sparking incident to the controlthereof through. the intermediary of mechanical relaysi 11. 'In'a signaling system, a thermionic device having a grid and a filament, means coinp-rising aipl urality of voltage sources 'for, negatively biasing the grid with referenceto the filament,said sources having impedance devices connected in shuntthereto, a thermi signaling system, a thermionic onic tube so associated with certain of said atively biasing said grid with respect to said filament to a potential proper for enicient operation of said device, means for applying enough additional biasing potential to render the device inoperative, said several biasing means being serially interposed between said grid and said filament, and means, including a thermionic tube, for establishing a shunt path around said second-mentioned biasing means;

13. In a signaling system, a thermionic device having a controlelectrode, a circuit net work associatedwith said. controLelectr'ode and including a potential source for apply ing a blocking potential thereto, thermionic by-pass means connected in shunt relation to a portion of said network through which flowscurrent from said source, and means for controlling ,the conductivity of said by pass means. i

In testimony whereof, I have hereunto subscribed my name this 22nd day of March, 1928. i

ROBERT DAVIS; 

